1. Field of the Invention
The present invention relates to an hydraulic system, particularly for motor vehicles, including a master cylinder, a slave cylinder, a connecting pressure-medium conduit, as well as a pressure relief valve that is integrated into the hydraulic system and that is governed as a function of the pressure of the pressure medium.
2. Description of the Related Art
Such hydraulic systems are utilized particularly in motor vehicles as arrangements to operate brakes, as power steering systems, and as arrangements to operate friction clutches, for example in the power flow between an internal-combustion engine and a transmission, and/or an electric motor and a drive train. Dampers such as are shown in British patent No. 2,032,581 are utilized for damping pressure pulses in the pressure medium. Such damping devices include at least one closing element that is axially actuated by an energy accumulator and which, when a predetermined closure pressure is exceeded, will produce a connection between the two elements. Such arrangements are especially susceptible to periodically recurring pressure pulses in the pressure medium and react to such stimulation with, for example, screeching noises. Moreover, the sealing seats of the closure elements are susceptible to soiling, so that absolute sealing of the pressure relief valve is frequently unattainable over its lifetime.
Such situations can be a drawback if pressure conditions within the hydraulic system change, caused for example by temperature changes. Changing pressure conditions develop in the conduit before and after the pressure relief valve, so that non-negligible flows of pressure medium can take place in the hydraulic system, which can increase the moisture level in the pressure medium and therewith as a consequence can impair the quality of the pressure medium.
It is therefore an object of the present invention to provide an hydraulic system in which damping of pressure oscillations that are introduced into the pressurized medium can take place, and one that produces improved operation relative to reducing induced noises, that is more economical to manufacture, that tightly seals secondary conduits of the hydraulic system, and that is easier to assemble. Furthermore, the hydraulic system is to be filled completely through one filling point.
The object is achieved by an hydraulic system that includes a slave cylinder, a master cylinder, a pressure-medium line connecting the cylinders, as well as at least one pressure-medium controlled pressure-relief valve integrated into the system, with at least two connections for inlet and outlet of pressure medium and at least one port connecting the inlet and outlet and that is sealingly closable by an elastic element.
The port, whose one opening points in the outlet direction and whose other opening points in the inlet direction, thereby advantageously has closed by an elastic body its opening that points away from the direction of the pressure, for example in the form of an opening-spanning elastic tube valve. If a pressure is applied from the first connection through the port in the direction of the opening that is closed by the elastic, at least part of the elastic body will be displaced by the pressing force of the pressure medium and a path of pressure medium is formed away from the opening in the direction of the second connection.
The closing pressure of such a valve is determined at least by the tension force in the elastic body, by which it presses closed the opening. Furthermore, the type and extent of the closing pressure between the bearing surfaces, against which the elastic body presses, and the pressure medium path formed by the elastic body, depends upon the type and arrangement of such as, for example, the diameter of the opening, the elastic modulus of the elastic body. As well, the surface characteristics of the elastic body and the bearing surfaces can enter into the magnitude of the closing pressure and the damping characteristics. In that manner pressure spikes can be damped and the pressure relief valve can be adapted to prevailing conditions and can be matched with them. The return movement of the elastic body against the opening and the surrounding material after the decline of the pressure spike ideally is elastic, and when compared with the impact of a spring-loaded sealing element on a valve seat it is practically noiseless.
An advantageous embodiment provides an arrangement of the connections that is approximately coaxial, whereby both connections can be placed in communication with each other by a predominantly radially-extending port. It is especially advantageousxe2x80x94by a radially nested arrangement of the chambers that communicate with respective terminal ends of the port, which chambers communicate with the connectionsxe2x80x94that the approximately coaxial connections are axially spaced from each other, so that at least one pressure relief valve in accordance with the invention can be arranged axially between the two connections, in which a port is formed between the respective connections to the axially adjacent chambers, one that provides communication between the two connections, whereby an elastic body is arranged on an opening of the port that closes the opening as a function of the pressure of the pressure medium. The port can thereby run substantially radially from one terminal end to the other, that is, that one terminal end communicates with one chamber, or extends to it, and that it extends radially further than the chamber of the second terminal end and that forms a port that leads from radially outside to radially inside to provide communication between the two chambers.
It is to be understood that in addition the chambers can be axially overlapped by the use of a common wall, for example, a sleeve-shaped wall that is closed at one end, and the port in its radial extent also can have axial portions and can be inclined from outside to inside, or can be provided as an axially-formed open slot in the common wall, through which a simpler structure can be achieved by means of an injection molding process, and by which radial undercuts can be avoided. By the use of a sleeve-shaped construction of the common wall between the first and second connections, in each case at lease one wall surface can be cylindrically constructed and on those cylindrical surfaces, inner or outer cylindrical surfaces, the elastic body can be sealingly applied over the discharge opening. It has proved to be especially advantageous in addition to utilize tube sections, which are pulled onto the outer cylindrical surface or are putxe2x80x94introduce into the inner cylindrical surface to seal radially outwardly.
The tube sections can each be formed as an insertxe2x80x94on the inner cylinder or on the outer cylinderxe2x80x94for different respective opening pressures, whereby experience has shown that for the arrangement of the tube section on the inner cylinder less closing pressure is required, that is, it opens at a lower pressure of the pressure medium. Both arrangements can be constructed to be self-reinforcing, that is, the sealing function can be reinforced by counterpressure in dependence upon the applied pressure of the pressure medium. For special application cases, the bearing surfaces of the elastic body can be formed with grooves to avoid self-reinforcement and to ensure a minimal flow of pressure medium.
All kinds of elastic materials can be advantageous for the elastic body, materials that are resistant to the pressure medium, for example, brake fluid of the customary specification, and especially materials that have no negative adhesive effects such as bonding, vulcanization, adhesion, and the like with the material from which the housing is formed, which can be composed of metal, ceramic, plastic, and the like, to receive the at least one pressure relief valve. Advantageous materials have proved to be plastics, preferably elastomers, rubber, and silicon, such as silicon rubber or silicon resin. When utilizing tube sections those materials can be drawn as tubes and suitably outfitted as an insert or as finished parts, for example cast, injected, or extruded, or pressed from laminated plastic, or sawed by means of a water- or laser-beam process.
Materials for producing the elastic bodies, especially tube sections, can be reinforced, for example by means of fabrics such as textile or steel cloth and the like, or by means of spirals or rings incorporated in or installed on the surface, and which can be composed of plastic or metal. Furthermore, it can be advantageous to utilize multi-ply or multi-layer formed tube sections whereby, by way of example, the separate functions, one of providing a component that seals the opening well and one of providing a shape-conforming component, can be combined to provide increased sturdiness. For additional applications it can furthermore be advantageous to construct the elastic bodies under prestress, by way of example, a tube section arranged on an outer cylindrical surface.
It can further be advantageous to secure the hose segment against axial slippage. For that purpose one configuration can have axial stops and/or, by the application of a groove in the outer cylindrical surface over which a tube section is drawn, which extends around the periphery particularly in the area where an axial end of the tube section is inserted on the cylindrical surface, and in which the end of the tube section can be drawn, whereby it can be especially advantageous to provide a circumferential bead or a bead segment at the inner circumferential side end, which is radially gripped in the groove. Alternatively or additionally, an axially aligned, circumferential shoulder, or circumferential segments, can be provided at a radial spacing from the cylindrical surfacesxe2x80x94the outer or the inner cylindrical surfacexe2x80x94to allow squeezing or clamping of the tube section between it and the cylindrical surface. It is to be understood that other fastening means, such as hose clamps, cable ties, and clamping rings can likewise be advantageous, nevertheless causing additional part costs.
In a further inventive concept that can provide an especial advantage, at least two pressure relief valves can be provided between two connections, whereby they can be arranged in an advantageous way to operate in opposition. That arrangement can thereby be provided in a separate housing that can be placed in a pressure medium conduit, or it can be integrated into a functional component that is part of an hydraulic system, for example a master cylinder or a slave cylinder, whereby relevant to the number of components especially suitable arrangements can be constructed.
The arrangement of two or more pressure relief valves in one housing provides in an especially advantageous way a so-called xe2x80x9cpulsation filterxe2x80x9d of a higher grade, thereby effective bi-directional damping of the transient pressure of the pressure medium can be obtained along with bi-directional filtration. Those damping arrangements can be especially advantageously arranged when they are provided with damped pressure relief valves in accordance with the invention. In addition, at least two ports can form one connection in one housing between two end connections, whereby at least one port is in contact with an elastic body of a first pressure relief valve and at least one further port is formed in contact with an elastic body of a second pressure relief valve.
It can thereby be advantageous to arrange both pressure relief valves axially spaced from each other, and/or the elastic bodies can be provided as tube sections, whereby in one pressure direction a tube section can be arranged on an outer cylindrical surface and in the other pressure direction a tube section can be arranged on the inner cylindrical surface. In doing so, in especially advantageous arrangements the pressure direction away from one slave cylinderxe2x80x94especially with a disengagement apparatus of a clutch with corresponding input of pressure pulses from the internal combustion enginexe2x80x94is damped by a pressure relief valve whose opening is closed by a tube section that is forced on the outer cylindrical surface, because a higher closing pressure can be achieved in the regulation by the application of comparable materials for tube sections, in comparison with a seal on the inner cylindrical surface. In each case the inner tube valve that is opened in the opposite pressure direction can seal in a self-reinforcing manner in the other pressure direction. By the selection of the materials and/or the installation geometry different or approximately equal opening pressures and pressure gradients can be adjusted for both pressure directions.
A further embodiment can be provided in which tube sections with approximately equal diameters are utilized, whereby the housing geometry is correspondingly proportioned.
A separately mounted pulsation filter, preferably with two oppositely-operating pressure relief valves, can be provided in one housing that is formed from at least two housing parts, which seal against each other and are axially supported. For sealing, conventional sealing means, for example an O-ring, can be utilized. Both parts can be axially connected by a further part, for example a casing, whereby the casing in each case radially engages a radially-projecting stop and that axially overlaps the connected parts. Furthermore, the housing parts can be connected together with a detent or snap connection or a bayonet catch. Advantageously at least one housing part is produced from plastic, for example by an injection molding process. Thereby the accommodations such as cylindrical walls for the elastic bodies, such as tube sections, connection means for the housing parts, such as detent hooks, bayonet hitches, and/or radial shoulders for connection means can already be formed. Furthermore, in at least one of the two parts a rotation guard against relative rotation of the housing parts with respect to each other can be provided.
Furthermore, based upon the inventive concepts it is especially advantageous to form an hydraulic system with at least one pressure relief valve having end connections joined with two conduit lines that are separated from each other and to simplify the filling operation for filling with pressure medium before starting, that the hydraulic system can be completely filled from a single filling opening, for example under the application of vacuum. In addition, in accordance with the invention a bypass is provided between the two conduit lines, that is, a bypass is made possible through the pressure medium in a range when the pressure relief valves are closed. This bypass is so arranged that it is opened only at the time of the filling procedure, and automatically closes after the filling procedure is stopped.
In addition, a seal can be provided parallel to the at least one pressure relief valve, which first becomes operational after contact with the pressure medium. For the seal, materials can be provided that swell upon contact with the pressure medium and that consequently close a gap that serves as a bypass, through swelling after contact with the pressure medium. The seal can thereby be so shaped that it allows a gap radially inside and/or radially outside, which is closed after the swelling process. Especially advantageous hereby is an insert of NBR (nitrile butadiene rubber), whereby the pressure medium is advantageously brake fluid or the like. Thereby the seal can radially seal both housing halves, whereby it can be arranged axially adjacent to a housing seal, which seals both housing parts from the outside, and between the two seals axially joins the inlet and outlet sides of a port, until the seal is swollen after the filling process and both connection ends are sealingly separated from each other, and thereby activates the at least one pressure relief valve.
Especially advantageous arrangements of an hydraulic system in accordance with the invention can be disengagement devices for hydraulically-operated friction clutches, braking devices, steering devices, and/or the like. It can be especially advantageous in the design of clutch release devices to tune the hydraulic system to damp frequencies in the region below one kiloherz, particularly between 60 and 80 Hz and especially between 80 and 100 Hz, in which range especially wavering and/or axial vibrations of the internal combustion engine are transmitted through the crankshaft to the disengagement system.
It can be especially advantageous in clutch disengagement devices when the closing pressure of a pulsation filter with oppositely operating pressure relief valves is so balanced that in the direction of the slave cylinder a residual pressure remains in effect, so that, for example, the entry of air bubbles into the conduit branch of the slave cylinder can be prevented. By this means there can be not only a reduction of effectiveness as a result of the increased compressibility resulting from the air bubbles, but moisture transfer can also be reduced, which, as experience has shown, by those air bubbles having a temperature-dependent degree of moisture, the moisture can enter the pressure medium and therewith the quality of the pressure medium can be drastically impaired, especially in the region of a poorly flushed slave cylinder, and therewith the operational reliability of the disengagement system can be endangered, especially at high temperatures.
It has proved to be advantageous to utilize pulsation filters with comparatively tightly disposed tube valves, in contrast to pulsation filters with closing bodies and valve seal seats. Advantageously the admission pressure, which operates the slave cylinder through the opening pressure of the pressure relief valve, which operates to block the outlet from the master cylinder, is adjustable. Preferably the pressure relief valve is constructed as a tube valve that has a tube section arranged on an outer cylindrical surface, that thereby can deliver higher admission pressures. It is to be understood that the admission pressure is kept small enough that in the slave cylinder is practically not axially shifted and the clutch is not axially impacted.